图像处理之Hessian矩阵提取关键点

- created by gloomyfish

一：大致的算法流程

1. 对每个像素点计算图像在X方向Y方向的二阶偏导数，计算图像的XY方向的导数

2. 根据第一步的计算结果，有Hessian Matrix计算D(h) = Ixx*Iyy - Ixy*Ixy

其中Ixx表示X方向的二阶偏导数

Iyy表示Y方向的二阶偏导数

Ixy表XY方向的二阶导数

3. 根据第二步计算出来的值使用3×3窗口实现非最大信号压制，

我的做法， 直接给了threshold值，这个其实不很对，真的懒，不想弄啦！

二：导数计算实现

关于一阶与二阶高斯偏导数计算请看这里：

http://blog.csdn.net/jia20003/article/details/16369143

三：程序效果

四：算法代码

package com.gloomyfish.image.harris.corner;    import java.awt.image.BufferedImage;  import java.util.ArrayList;  import java.util.List;    import com.gloomyfish.filter.study.AbstractBufferedImageOp;    public class HessianFeatureDetector extends AbstractBufferedImageOp {            private GaussianDerivativeFilter gdFilter;      private double minRejectThreshold = 4.1; // (r+1)^2/r      private List<HessianMatrix> pixelMatrixList;            public HessianFeatureDetector()      {          gdFilter = new GaussianDerivativeFilter();          pixelMatrixList = new ArrayList<HessianMatrix>();      }            @Override      public BufferedImage filter(BufferedImage src, BufferedImage dest) {          int width = src.getWidth();          int height = src.getHeight();          initSettings(height, width);          if ( dest == null )              dest = createCompatibleDestImage( src, null );            int[] inPixels = new int[width*height];          gdFilter.setDirectionType(GaussianDerivativeFilter.XX_DIRECTION);          BufferedImage bixx = gdFilter.filter(src, null);          getRGB( bixx, 0, 0, width, height, inPixels );          extractPixelData(inPixels, GaussianDerivativeFilter.XX_DIRECTION, height, width);                    // YY Direction          gdFilter.setDirectionType(GaussianDerivativeFilter.YY_DIRECTION);          BufferedImage biyy = gdFilter.filter(src, null);          getRGB( biyy, 0, 0, width, height, inPixels );          extractPixelData(inPixels, GaussianDerivativeFilter.YY_DIRECTION, height, width);                    // XY Direction          gdFilter.setDirectionType(GaussianDerivativeFilter.XY_DIRECTION);          BufferedImage bixy = gdFilter.filter(src, null);          getRGB( bixy, 0, 0, width, height, inPixels );          extractPixelData(inPixels, GaussianDerivativeFilter.XY_DIRECTION, height, width);                    int[] outPixels = new int[width*height];          int index = 0;          for(int row=0; row<height; row++) {              int ta = 0, tr = 0, tg = 0, tb = 0;              for(int col=0; col<width; col++) {                  index = row * width + col;                  ta = 255;                  HessianMatrix hm = pixelMatrixList.get(index);                  double[] t = hm.getThreshold();                  if(t[0] > minRejectThreshold)                  {                      tr = 127;                  }                  else                  {                      tr = 0;                  }                  if(t[1] > minRejectThreshold)                  {                      tg = 127;                  }                  else                  {                      tg = 0;                  }                  if(t[2] > minRejectThreshold)                  {                      tb = 127;                  }                  else                  {                      tb = 0;                  }                  outPixels[index] = (ta << 24) | (tr << 16) | (tg << 8) | tb;              }          }            setRGB( dest, 0, 0, width, height, outPixels );          return dest;      }            private void initSettings(int height, int width)      {          int index = 0;          for(int row=0; row<height; row++) {              for(int col=0; col<width; col++) {                  index = row * width + col;                  HessianMatrix matrix = new HessianMatrix();                  pixelMatrixList.add(index, matrix);              }          }      }            private void extractPixelData(int[] pixels, int type, int height, int width)      {          int index = 0;          for(int row=0; row<height; row++) {              int ta = 0, tr = 0, tg = 0, tb = 0;              for(int col=0; col<width; col++) {                  index = row * width + col;                  ta = (pixels[index] >> 24) & 0xff;                  tr = (pixels[index] >> 16) & 0xff;                  tg = (pixels[index] >> 8) & 0xff;                  tb = pixels[index] & 0xff;                  HessianMatrix matrix = pixelMatrixList.get(index);                  if(type == GaussianDerivativeFilter.XX_DIRECTION)                  {                      matrix.setXx(new double[]{tr, tg, tb});                  }                  if(type == GaussianDerivativeFilter.YY_DIRECTION)                  {                      matrix.setYy(new double[]{tr, tg, tb});                  }                  if(type == GaussianDerivativeFilter.XY_DIRECTION)                  {                      matrix.setXy(new double[]{tr, tg, tb});                  }              }          }      }    }